Don't unnecessary fail to parse reply when pulling images

Reply from podman is somewhat like this:
```
$ sudo curl -X POST --unix-socket /run/podman/podman.sock http://d/v1.24/libpod/images/pull?reference=fedora
{"stream":"Resolved short name \"fedora\" to a recorded short-name alias (origin: /etc/containers/registries.conf.d/shortnames.conf)\n"}
{"stream":"Trying to pull registry.fedoraproject.org/fedora:latest...\n"}
{"stream":"Getting image source signatures\n"}
{"stream":"Copying blob sha256:8fde7942e775327f2d6ddaf08f45fda74201a7769951b0413860e21b59b4bf82\n"}
{"stream":"Copying config sha256:79fd58dc76113dac76a120f22cadecc3b2d1794b414f90ea368cf66096700053\n"}
{"stream":"Writing manifest to image destination\n"}
{"stream":"Storing signatures\n"}
{"images":["79fd58dc76113dac76a120f22cadecc3b2d1794b414f90ea368cf66096700053"]}
{"id":"79fd58dc76113dac76a120f22cadecc3b2d1794b414f90ea368cf66096700053"}
```
Since it is not a single JSON object we fail to parse it. But we don't really
care about any of it, so let's not parse it.

Fixes #640

src/client.js

@@ -256,7 +256,7 @@ export function pullImage(system, reference) {
             reference: reference,
         };
         podmanCall("libpod/images/pull", "POST", options, system)
-                .then(reply => resolve(JSON.parse(reply)))
+                .then(resolve)
                 .catch(reject);
     });
 }